1. Field of the Invention
The present invention is concerned in one aspect with a resettable vacuum-type switch interrupter especially designed for protecting electrical distribution circuits from the effects of fault currents. In another aspect, the invention comprehends a full range protective device including the resettable vacuum switch along with a series-related current limiting fuse (CLF) to give a coordinated, full range protective device. The switch interrupter component has a number of unique features which render it particularly advantageous for use in oil-filled equipment such as padmounted switchgear and the like. Such features include the preferred violence-and contamination-free operation of the interrupter, high mechanical advantage weld breaking capabilities in both the manual and fault-produced modes of switch contact opening so as to positively assure that the switch contacts open, and gang operation of respective switches in a three-phase system so as to prevent a situation where the current path through one phase conductor is broken while the remaining two phase conductors remain energized.
2. Description of the Prior Art
U.S. Pat. No. 4,083,028 (which is hereby incorporated by reference herein) discloses a double-fused vacuum switchgear used in the fault protection of electrical distribution circuitry. Broadly speaking, the apparatus disclosed in this patent includes a fuse assembly having a current limiting fuse and an expulsion-type fuse link in series. The fuse assembly is in turn coupled in series with a switch element in a dielectric filled tank. The apparatus disclosed in U.S. Pat. No. 4,083,028 represents a significant breakthrough in the art and provides excellent, full range coordinated circuit protection. However, the subject device has an electrical duty rating making it inappropriate for use in some modern day high voltage and amperage systems. For example, the prior device is admirably suited for protecting distribution circuits rated at 15 kV and up to 200 amps, but is not designed for higher rated systems now coming into use, e.g., 35 kV and 200 amps or more.
For example, if an expulsion-type fuse link-CLF arrangement is used in such higher rated systems, fault-induced fusing of the link may significantly contaminate the surrounding dielectric material and may also be unacceptably violent. Further, in three-phase circuits only a single phase may be interrupted by fuse actuation, while the remaining phases are energized. This is dangerous inasmuch as downstream three-phase electrical equipment can be damaged or destroyed in such a case. This single phase fusing problem is compounded because no indication is given of which phase conductor has experienced the fault, thereby necessitating time-consuming checking of all of the protective devices associated with each phase conductor after every fault occurrence.
Also, it will be appreciated that the device disclosed in U.S. Pat. No. 4,083,028 is not resettable; that is to say, actuation of the low range fuse link necessitates manual removal of the fuse assembly from the tank and replacement of the link. This represents a cost both in terms of replacement fuses but more importantly in time and labor.
Finally, the fuse link-CLF protective combination cannot be used as a load break switching element without considerable modification and expense. This latter factor is particularly pertinent when it is considered that the recent trend is to prohibit manual load break operations (e.g., by simply grasping an external load break elbow with a hotline tool and pulling on the same to break the load), so that the capability of breaking loads without resorting to manual expedients would be a significant advantage.
There is accordingly a real need in the art for an improved system for protecting higher rated electrical distribution circuits and which overcomes the potential problems of oil contamination, violent operation, single phase fusing, load breaking and lack of easy resettability.